It is important for discovery and treatment of various diseases to know biological information such as glucose concentration in blood. In order to determine the biological information in blood, a method using an analytical tool such as a biosensor is known. This method involves supplying a reagent layer in the analytical tool with a blood sample, and detecting information corresponding to a concentration of a target ingredient in the blood sample based on a reaction product as a result of reaction of the blood sample with a reagent, in a concentration measuring apparatus using an optical method or an electrochemical method.
In such a concentration measuring apparatus, it is necessary to check whether or not the apparatus operates normally to ensure reliability of a measurement result when the apparatus has not been used for a long time, or every certain period. Usually, a check of a concentration measuring apparatus is performed by a user by installing an analytical tool in the apparatus while manually selecting a control solution measurement mode by operating the concentration measuring apparatus, and supplying the analytical tool with a control solution.
In such a method, the user needs not only to make operation for carrying out an operation check of the apparatus, but also to make operation for returning the apparatus to a normal measurement mode after completion of the operation check of the apparatus, and hence has a big burden. This may lead a situation that the apparatus is checked without switching the mode from the normal measurement mode to the control solution measurement mode, or that the sample is measured without switching the mode from the control measurement mode to the normal measurement mode. As a result of this, a correct check result or measurement result is not obtained, and the necessity of recheck or re-measurement may arise.
In order to solve such a drawback, it has been proposed to automatically recognize a control solution and to check the apparatus in a concentration measuring apparatus (see, Patent documents 1 to 3, for example).
The method described in Patent document 1 focuses on a difference in solubility between whole blood and control solution in a reagent layer, and discriminates the control solution from the whole blood based on profiles of reflectance. This method is applied to a measurement system utilizing an optical technique, and a control solution containing an IR pigment having maximum absorption at a wavelength different from a measurement wavelength is used, discrimination between whole blood and a control solution is made at a wavelength different from the measurement wavelength.
In Patent document 1, there is also disclosed a method for discriminating a control solution from whole blood based on a difference in a measured current value between the whole blood and the control solution in a measurement system using an electrochemical technique.
In Patent document 2, likewise Patent document 1, there is disclosed a method for discriminating a control solution from whole blood based on profiles of reflectance in a measurement system using an optical technique, and also disclosed a method for discriminating a control solution from whole blood based on a difference in a measured current value in a measurement system using an electrochemical technique.
In the method described in Patent document 3, for an electrode-type biosensor, a detection electrode is provided in addition to an active electrode and a counter electrode, and a control solution is automatically discriminated based on oxidation current obtained by using the detection electrode, in a measurement system using an electrochemical technique. The methods of the foregoing documents focus on a fact that behavior of the oxidation current obtained when the control solution reacts with the reagent layer of the biosensor differs from behavior of the oxidation current obtained when the sample reacts with the reagent layer, and automatically discriminates the control solution from the sample based on an oxidation current value after a lapse of a predetermined time, or time-varying change in an oxidation current value.
However, the method for discriminating a control solution based on profile of reflectance as described in Patent documents 1 and 2 will be influenced by solubility in the reagent layer or reaction speed. On the other hand, since solubility in the reagent layer or reaction speed vary between different biosensors, and may vary during the period from production till use. When whole blood is used as a sample, reflectance will be influenced by a hematocrit value of the whole blood. Therefore, in the method for discriminating a control solution based on profile of reflectance, it is difficult to accurately discriminate the control solution.
Further, the method for discriminating a control solution based on a measured current value in a measurement system using an electrochemical technique is not applicable to a measurement system using an optical technique.
Patent document 1: Japanese Patent Application Laid-Open Publication No. 2003-114214
Patent document 2: Japanese Patent Application Laid-Open Publication No. 2005-531760
patent document 3: Japanese Patent Application Laid-Open Publication No. 2001-208718